This invention relates to a polymer electrolyte membrane fuel cell having distributor plates made of an elastic, plastically deformable and electrically conductive material.
In the simplest case, fuel cells consist of two electrically conductive electrodes which are separated from one another by an ion-conducting membrane. For feeding the reaction media, distributor plates having integrated gas or liquid feeding ducts are used. In order to prevent an uncontrolled escape of the reaction media, the individual gas or liquid spaces in the case of conventional fuel cells are sealed off with respect to one another by means of seals which are each arranged between the distributor plates and the electrodes.
In the case of fuel cells with proton-conducting polymer electrolyte membrane (so-called PEM fuel cells), the distributor plates are made of graphite materials, and seals made of an elastomer material are entered into the porous electrodes of the membrane electrode arrangement which consist of carbon paper. For the distributor plates, elastic, plastically deformable and electrically conductive materials can preferably be used, particularly graphite foils with a specific density of 0.2-1.8 g/cm.sup.3. Such an arrangement is shown, for example, in U.S. Pat. No. 5,284,718.
Since the distributor plates and elastomer seals are made of different materials, they have different thermomechanical characteristics. Thus, during the operation of the PEM fuel cell, leakages can occur as a result of the heating of the fuel cell because of the different expansion of the materials. In addition, considerable expenditures are required for the manufacture, mounting and precise adjustment of these seals.
In order to solve this problem, it was suggested in German Patent Document DE 43 14 745 C1 to manufacture all important components of the PEM fuel cell (and thus also the distributor plates) of a thermoplastic basic polymer, and to join them by means of a combining process without any additional sealing material. Although this method eliminates the need for separate elastomer seals, it considerably limits the selection of material for the fuel cell construction.
It is an object of the present invention to provide an effective and easily manufacturable sealing arrangement for polymer electrolyte membrane fuel cells having distributor plates made of an elastic, plastically deformable and electrically conductive material.
According to the invention, this object is achieved providing the seal in the form of an elevated portion which is integrated into the distributor plate itself. This arrangement offers various advantages. On the one hand, the thermomechanical characteristics of the sealing material and of the distributor plate are identical, and are thus not critical with respect to a heat expansion. In addition, the manufacture of the distributor plates and the construction of the seal can take place in a common fabrication process, which reduces the manufacturing costs. Finally, the expenditures for the mounting and precise adjustment of the seal are eliminated.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.